Solo 401k Contribution calculation

[myn7055]

I had a W2 job for the first half of the year. I made around $50,000 and contributed $10,000 to a regular 401k. I started working as a contractor in December, and my profit was $5,000 for 2024. What’s the max I can contribute to a solo 401k as an employee for 2024? I’m under 50 and the limit is $23,000. Can I contribute $13,000 ($23,000 - $10,000)? According to a solo 401k contribution calculator, the maximum contribution that I can defer into my solo 401k is $4,646. Is this correct?

[dmertz · Accepted solution]

The individual's limit on elective deferrals is not the only limit.  There is also a per-plan limit on additions.  Your additions to the solo 401(k) are not permitted to exceed your net earnings from self employment.  Net earnings are net profit minus the deductible portion of self-employment taxes.

Net earning in this case are,

$5.000.00 - ($5.000.00 * 0.9235 * 0.153) / 2 = $4,646.76

so your additions to your account in the solo 401(k) plan are limited to $4,646.76.

[dmertz · Accepted solution]

If you round the result at each step, which is what happens on TurboTax's Keogh, SEP and SIMPLE Contribution Worksheet, the calculation becomes:

Round($5,000 * 0.9235) = $4,618

Round($4,618 * 0.153) = $707

Round($707 / 2) = $354

$5000 - $354 = $4,646